The present invention relates to the field of magnetic field sensors, and in particular to an offset-compensated Hall sensor.
The publication “Auto & Elektronik” dated 4/2000, pages 19–23, discloses a Hall sensor that includes a complete integrated system, including the actual Hall sensor. The area of application is designed for the voltage range 100 μV–1 mV at magnetic field strengths of 2–20 mT. As a result, Hall sensors of this type are susceptible to offset drifts that may occur in response to changes in temperature and fluctuations in voltage, but which may also occur as a result of mechanical stress which the package, for example, transfers to the chip, or due to other factors. To reduce this offset, a so-called chopper method is provided, also known as the “zero-drift principle.” In this method, the current direction of the Hall current through the Hall plate forming the actual sensor element is continually switched. Any corruptions in the measurement signal produced, for example, by geometrical distortions in the Hall plate, are incorporated into the measured value independently of the current direction, but are then either added or subtracted as a function of the current direction. Since both measurements are performed through identical structures having the same stress profile, the offset produced by mechanical stresses of the package is averaged out. With addition of the Hall voltages determined by the two Hall voltages with different directions of current flow, an alternating-voltage component indicates the offset while the direct current indicates the offset-compensated Hall voltage. In the case of subtraction, the reverse is true.
These vertical Hall sensors, in which taps are arranged on the surface of the Hall sensor element to feed in and feed out the Hall sensor current and to determine the Hall voltage, are principally employed to measure magnetic fluxes parallel to a planar crystal surface. As a result, two orthogonal field vectors can be measured with one chip. Methods of this type are employed in position sensors or rotary encoders. Due to offset voltages, however, the properties of currently known vertical sensors are often very inaccurate and are thus not considered for many possible applications.
Therefore, there is a need for a Hall sensor or method for determining an offset-reduced Hall voltage, which sensor or method provides a further reduction in offset voltages.